1. Field of the Invention
The present invention relates to an objective lens position detecting system which detects the position of an objective lens shifting in an optical head for use in, for example, a disk apparatus.
2. Description of the Related Art
Various disk apparatuses have been developed which cause a semiconductor laser oscillator (light source) in an optical head to irradiate a laser beam on an optical disk to record data on the optical disk, or convert data recorded on the optical disk into an electric signal by means of a detector provided in the optical head and then convert the signal into a video signal before reading it out.
Such optical disk apparatuses have a coarse access mode to roughly access an optical disk by moving the whole optical head and a fine access mode for finer access by moving an objective lens in the optical head.
When the whole optical head is moved in coarse access mode, the objective lens in the optical head vibrates. To prevent or suppress this vibration, the moving position of the objective lens is detected and the objective lens is held at a predetermined position based on a detection-reflecting signal in fine access mode.
A circuit for detecting the moving position of the objective lens outputs a detection signal corresponding to the amount of movement (moved distance) to a reflector that moves together with the objective lens, in accordance with the amount of light from the light source reflected or shielded by the reflector.
This detection circuit cannot however acquire an accurate detection signal when the amount of radiation from the light source (light-emitting element) varies due to dust or the ambient temperature.